The present invention relates to a bicycle brake device with which brake shoes are pressed against a wheel to effect braking by moving an inner cable positioned inside an outer casing.
A bicycle brake device generally involves the pressing of brake shoes against a wheel to effect braking by using a brake lever provided to the handlebar to move an inner cable positioned inside an outer casing. The brake shoes are supported by a pair of brake links, and the brake links usually are operated by one of two methods: center pull and side pull. In the center-pull type of brake device, which is used primarily in cantilevered brake devices, an inner cable that is branched in two is attached to the distal ends of the two brake links, and the outer casing is attached to the bicycle frame. In the side-pull type of brake device, used primarily in caliper type brake devices, the inner cable and the outer casing each are attached to a brake link.
Cantilevered brake devices with the same cable connection configuration as the side-pull type of brake device (that is, the inner cable and the outer casing each are attached to a brake link) have been put to practical use in recent years. These are high-performance brake devices with improved braking performance, and the change in the braking force with respect to the amount of movement of the inner cable (cable stroke) after the brake shoes contact the rim (hereinafter referred to as the braking characteristic) is greater than with a conventional design. As a result, the braking force tends to increase suddenly with only very slight brake lever operation. This makes braking difficult for a beginner who is unfamiliar with the brake lever operation. Also, if the braking force on the rear wheel increases suddenly, then when fine brake lever operation is impossible because of the gap between the brake shoes and the wheel in a cross-country race, for example, the rear wheel will slip and the bicycle will be difficult for even an advanced rider to control.
One possible way to prevent the above problem is to reduce the braking characteristic of the brake lever during braking. This has been put into practice in the operating force transmission device disclosed in Japanese Laid-Open Patent Application 63-203491. This operating force transmission device is provided with a control spring in the cable axial direction somewhere along the operating cable, which is composed of an inner cable and an outer casing, and is also provided with an adjuster for adjusting the spring force of the control spring. This control spring bends under the brake actuation load, so the output with respect to the input to the brake links is reduced, which allows the braking characteristic to be decreased.
If an operating force transmission device such as this is provided at some point along the operating cable, then when the spring force (bias force) at which the control spring begins to bend is suitably adjusted, the control spring will begin to bend during braking when the tension on the cable becomes greater than the biasing force of the control spring. As a result, the braking characteristic will be smaller, and sudden increases in the braking force during braking can be suppressed even with a high-performance brake device. Of course, the braking characteristic generally varies with the type of the brake device, its shape, and other such factors. Accordingly, the desired braking characteristic during braking will not be obtained unless a transmission device that matches the braking characteristic for the brake device in question is provided somewhere along the operating cable. Unfortunately, since the transmission device is provided separately from the brake device along the operating cable, a beginner could mistakenly mount a transmission device intended for a brake device with a different braking characteristic along the operating cable, in which case the desired braking characteristic during braking will not be obtained, and the brake actually may be more difficult to operate. Furthermore, the space in which the operating cable is laid is frequently relatively narrow so that the inner cable can move smoothly through the outer casing. Consequently, if a transmission device that is long in the cable axial direction is provided somewhere along the operating cable, then the degree of freedom with which the operating cable can be positioned will be reduced, making the operating cable layout more difficult to design.